The American Trucking Associations' advanced seasonally adjusted (SA) For-Hire Truck Tonnage Index fell 4.0 percent in January after surging 6.4 percent in December 2011. The latest contraction put the SA index at 119.4 (2000=100), down from December's record level of 124.4.
 

ATA recently revised the seasonally adjusted index back five years as part of its annual revision. For all of 2011, tonnage rose 5.8 percent, slightly lower than the 5.9 percent previously reported, and matched 2010's gain of the same magnitude. The index increased 3.6 percent from January 2011.
 

The not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 112.1 in January, which was 3.5 percent below the previous month.
 

"Last month I said I was surprised by the size of the gain in December. Today, I'm not surprised that tonnage fell on a seasonally adjusted basis in January simply due to the fact that December was so strong," ATA Chief Economist Bob Costello said. Costello noted that December's increase was the largest month-to-month gain since January 2005.
 

"I'm still optimistic about truck tonnage going forward. In fact, while many fleets said January was normal, they are also saying that February has been pretty good so far," he said.
 

Each month, ATA asks its membership the amount of tonnage each carrier hauled, including all types of freight. The indexes are calculated based on those responses. The sample includes an array of trucking companies, ranging from small fleets to multi-billion dollar carriers. When a company in the sample fails, its final month of operation is included and zeroed  out for the following month, with the assumption that the remaining carriers pick up that freight. As a result, it is close to a net wash and does not end up in a false increase. Nevertheless, some carriers are picking up freight from failures and it may have boosted the index. Due to the correction mentioned however, it should be limited.
 

Trucking serves as a barometer of the U.S. economy, representing 67.2 percent of tonnage carried by all modes of domestic freight transportation, including manufactured and retail goods. Trucks hauled 9 billion tons of freight in 2010. Motor carriers collected $563.4 billion, or 81.2 percent of total revenue earned by all transport modes.
 

ATA calculates the tonnage index based on surveys from its membership and has been doing so since the 1970s. This is a preliminary figure and subject to change in the final report issued around the 10th day of the month. The report includes month-to-month and year-over-year results, relevant economic comparisons, and key financial indicators.